Patent GB-190905081-A (GB)
Title: Improvements relating to Means for Rectifying Electric Currents.
Inventor: MURPHY THOMAS JOSEPH
IPC: H02M7/36
Filed: 1909-03-02
Granted: 1910-03-02
Abstract: 5081. Murphy, T. J. March 2. Converting alternating and direct currents; commutator switching - arrangements; transformers.-Means for converting variable electric currents into direct or unidirectional currents of the kind described in Specification 21,366/08 comprises a pair of electrodes, forming a gap across which the current is adapted to flow when the resistance of the gap is lowered by the highpotential discharge of a condenser which is directed by means of a vibrating contact-arm controlled by the variation in the current to be converted. As shown in Fig. 11, an alternating- current transformer 95 supplies unidirectional current to a translating-device 108 through airgaps 11, 12 and 13, 14, which are normally impassable. The main current leads 101, 103 are connected to the primary windings 87, 88 of two step-up transformers. The secondaries 89, 90 of these transformers are independently connected through reactances 118, 119 and 120, 121 to two condensers 116, 117, which thus receive a high-potential charge. The leads 101, 103 are also connected through the air-gaps formed by the electrodes 13, 14 and 11, 12 respectively by way of reactances 104, 105 with the translating-device 108, which is placed in circuit with the neutral lead 102. To discharge the condensers 116, 117 across the air-gaps 11, 12 and 13, 14 respectively, at suitable times, each condenser is shunted with one air - gap through contacts 43, 45 and 44, 46 respectively. A conductor 42 is fixed to an armature which oscillates under the influence of two magnets 54 excited by current from the main leads 101, 103. The armature is polarized by means of a magnet 33 constantly excited by connexion with the translating-device 108 or an independent battery, or by means of a permanent magnet. The conductor 42 consequently moves in unison with the variations of the electromotive force between the main leads 101, 103, and, as it passes in turn close to the contacts 43, 45 and 44, 46, discharges the condensers 116, 117 alternately across the air-gaps 13, 14 and 11, 12. The main current from each lead flows successively through the arcs thus produced, and maintains each are until the electromotive force of the alternating-current wave falls below a limiting value. To ensure regular rupture of the arcs, magnets 26, 27 are placed in series with the main leads and serve to keep the electrodes cool by moving the arcs over the electrode surfaces, also blowing them out at the required moment. Any other blast may be used, and in some cases none may be necessary. In these cases, ordinary choke-coils replace the magnets 26, 27. In order to control the phase-displacement of the discharge of the condensers 116, 117 with regard to the waves of electromotive force of the main current, an inductance device 109 is connected in series with the magnets 54. A rotatable arm 114 is arranged to sweep over studs, connected to points on an inductance 110 and a resistance 112 respectively, to connect them together, thus enabling the proportions of resistance and inductance in the operating circuit of the condenser-discharging device or circuit-controller to be varied, and regulating the phase-displacement. The system shown in Fig. 11 is there applied to charging a battery 108, and is controlled by two electro - magnetic switches 62, 63 arranged in series in the circuit of the condenser - charging transformers and of the discharging-device. To start the apparatus, it is necessary to close these switches by hand by releasing spring catches which hold the switches open after actuation by their magnets 58, 59 respectively. The magnet 58 is connected in shunt with the battery 108, and responds to a predetermined terminal potential-difference ot the latter. The magnet 59 is operated by current induced in secondary windings on the reactances 104, 105 when this exceeds a predetermined amount. The system may be operated on one half of the alternating - current wave by interrupting the discharging-circuit of one of the condensers. Fig. 1 shows the mechanical arrangement of the apparatus. The base 1 contains the transformers 87, 88 and the condensers and reactances used in connexion therewith. All are immersed in oil. A base 2 attached to the base 1 carries the circuit controller and the electromagnetic switches. A third base 3, supported above the foregoing, carries the electrodes 11 ... 14, the blow-out magnets 26, 27, and two graphite resistances 9, 10, which shunt the air-gaps 11, 12 and 13, 14 respectively. A housing 4 surmounts the whole. The electrodes 11 ... 14, which are preferably of graphite and have parallel arcing faces, are secured to four independent bridges mounted on pedestals on a base 82. The bridges carrying the outermost electrodes are adjustably secured to their pedestals so that the width of the air-gaps may be regulated. The magnets 26, 27 are laminated and mounted on the base 82 with their poles underneath and parallel to the faces of the electrodes. The circuit - controller is shown in plan in Fig. 4 and in elevation in Fig. 5. The base 32 supports a magnet 33, which has an horizontal pole 35 and a vertical pole 34 magnetically connected together. Pivoted on the latter by means of a bracket 38 is a softiron tongue 39, to which is attached by an insulating coupling a metallic rod 40 carrying a rod 42 of platinum. This moving system may be mounted between two stones to diminish friction. Supported by a bracket 53 fixed to the base is a laminated horseshoe magnet core 55 carrying the windings 54, its poles being slightly above and on either side of the tongue 39 when this is in alinement with the pole 35. Two uprights 49 of insulating-material, fixed in a yoke 51 adjustably attached to the base 32, carry four adjustable arms 47. These arms hold the platinum terminals 43 ... 46, and are secured by clamps 48 to the uprights, so that they may be adjusted with respect to the rod 42, or swung aside to interrupt the condenser - discharging circuit when rectifying half the alternating-current wave. One of the electro-magnetic switches is shown in Fig. 7, and Fig. 9 shows a detail in elevation. They each consist of an electro-magnet 59 secured to a common base 56, and have a pivoted armature 63 with an adjustable counterweight 67 for determining the current with which each will operate. The armature is arranged to depress a spring-supported contact 73 by means of a lug 71 carried by the armature, so severing the connexion between this contact and an adjustable contact 77. An adjustable stop 81 limits the upward movement of the armature, and a spring catch 126 holds the end of the armature down when it has operated. The poles of the magnets may be paraboloidal in order to increase the extent of movement of the armatures. To release the armatures, a spring-controlled plunger 128 connected to a cross-bar 127 is pulled outwardly. The switches may be enclosed in a glass case. Fig. 10 shows one of the transformers. The primary and secondary windings 87, 89 are wound on the same closed-circuit core, and a magnetic shunt 91 is interposed to protect the secondary on short-circuit. The primary windings of the two transformers are connected in parallel so that each may be practically unaffected by the flow of current in the other.